1. Field of Invention
The invention relates to a process for regenerating oxidation catalysts containing vanadium oxide.
It is known that complex catalysts containing vanadium oxide, which are used, for example, for the production of maleic anhydride by catalytic oxidation of butane with molecular oxygen, become deactivated with time. A process for reactivating these deactivated catalysts, by treatment with a reducing agent, is also known (German Offenlegungsschrift (Published Specification) 2,353,136). However, the recovered activity and selectivity of the catalyst does not last long, so that the reductive treatment must be repeated after only a relatively short time.
It is also known to convert the vanadium pentoxide, of the spent catalysts, into volatile vanadium oxychloride by treatment with thionyl chloride or phosgene, and to convert this compound into vanadium pentoxide in the usual manner. In an even better way, vanadium pentoxide may be recovered from catalysts which contain vanadium pentoxide by treating the catalysts with carbon tetrachloride at not less than 100.degree. C. and reacting the volatile reaction mixture with ammonia to give ammonium vanadate (German Offenlegungsschrift (Published Specification) 2,228,927). In these processes, the catalyst is not actually regenerated and instead only vanadium is selectively recovered, and at the same time auxiliary materials are consumed and problems of recovery or disposal both of the by-products resulting therefrom, and of the residual constituents of the catalyst, arise.
Accordingly, there is lacking a process which permits the regeneration of such catalysts in a technically simple manner. In this context, regeneration is generally understood as a process which makes it possible to obtain an active catalyst from a deactivated catalyst.